Method of fastening a fastening element to a workpiece

ABSTRACT

The present invention relates to a method of fastening a fastening element to a workpiece by means of a setting device, wherein the fastening element and/or the workpiece is/are at least sectionally reshaped during the fastening, and wherein a lubricant is used that is free of grease and free of oil, in particular with the lubricant being a substance mixture of two or more substances.

The invention relates to a method of fastening a fastening element to a workpiece by means of a setting device, wherein the fastening element and/or the workpiece is/are at least sectionally reshaped during the fastening.

Large loads usually occur in reshaping processes and can have a negative influence on the quality of the connection of the element to the workpiece. They also cause considerable wear of the tools involved.

Lubricating oils can indeed reduce the friction that occurs between the components to be connected and/or the tools used in methods of the initially named kind. However, their use suffers from disadvantages in many cases since they can have a disruptive effect in subsequent processing steps. The workpieces therefore have to be cleaned in a complex and/or expensive manner after the attachment of a fastening element, which is accompanied by considerable costs.

It is therefore an object of the present invention to provide a method of the initially named kind in which the loads on the components involved are reduced and which is more efficient.

The present invention is based on the surprising finding that a grease-free and oil-free lubricant provides good or even better results with respect to the lubrication than conventional lubricating oils. Such lubricants are usually less viscous than the previously used lubricating oils so that it would be expected that their lubricating effect is smaller than that of conventional lubricating oils. However, comprehensive and complex and/or expensive examinations prove that a surprisingly good lubricating effect is produced with oil-free and grease-free means under the conditions present with fastening methods of the initially named kind. It has even been shown that—compared to methods based on the use of lubricating oils or lubricating greases—less lubricant has to be used to achieve good and reliable connections between the fastening elements and the workpieces. This in turn means that the component assemblies produced come from the setting device with only small lubricant residues or even practically free of residue and that their subsequent handling is considerably simplified. Any residues can also be removed substantially more easily than lubricating oil residues or lubricating grease residues.

Such residues are namely, for example, problematic in painting work such as cathodic dip painting (CDP) in which the workpiece is placed into a paint bath and the paint is deposited at the workpiece due to an applied voltage. Lubricating oil residues or lubricating grease residues at the inserted workpieces very quickly lead to contamination of the paint bath. Such lubricating oil residues or lubricating grease residues frequently interfere with paint wetting so that deficient painting results can be the result.

A welding of workpieces that still have lubricating oil residues or lubricating grease residues is also hardly possible.

In addition, lubricating oils or lubricating greases are ecologically problematic, among other things. Their use means that complex units such as oil separators, oil pans and the like have to be present. The disposal, storage and handling of oil residues/grease residues are also complex and cost-intensive.

The surprising suitability of oil-free and grease-free lubricants in fastening processes of elements to workpieces in which reshaping processes are provided considerably reduces the necessity of the post-processing of the component assemblies obtained. Such lubricants yield more and/or evaporate more easily with the same process results. As a result of less residue, a cleaning step following the fastening process becomes simpler or can even be omitted under certain circumstances. Oil-free and grease-free lubricants are also less critical from an ecological viewpoint in many cases and can even be biodegradable under certain circumstances.

The supply of an oil-free and grease-free lubricant into the region where it is required is also simpler—not only due to the lower viscosity and the greater yield. Corresponding lubricant application devices can therefore be kept simpler in design.

The term lubricant is not to be understood as restrictive to the effect that the agent substantially only has a lubricating effect. It can also provide further functionalities. The lubricant can be a substance mixture that comprises two or more substances. The lubricant is preferably liquid. In general, a suitable lubricant emulsion or lubricant suspension can also be used. Solid lubricants can also be used, in particular as fine powders.

Further embodiments of the method in accordance with the invention are set forth in the description, in the claims, and in the enclosed drawings.

In accordance with an embodiment of the method, the fastening element and/or the workpiece is/are at least partly metallic at least in a region around a fastening point at which the fastening element is connected to the workpiece. The fastening element and/or the workpiece is/are in particular completely composed of metal. In the case of (partly) metallic materials, the loads occurring during the fastening process are particularly high so that the advantages of the method in accordance with the invention are particularly pronounced here.

The fastening element can be a rivet element and/or the workpiece can be a sheet metal part. Provision can generally be made that the workpiece is prepared for the reception of the element. It is pre-punched, for example. However, it is also possible to use the method for self-piercing elements.

The lubricant is in particular a water-soluble and/or water-based lubricant. Such lubricants are usually less expensive and less problematic from an ecological viewpoint.

In accordance with an embodiment of the method, the lubricant comprises a corrosion inhibitor and/or a wear protection additive so that the workpiece and/or the element automatically receives/receive a certain corrosion protection and/or wear protection by way of the fastening process.

In accordance with a further embodiment of the method, the lubricant is free of chlorine and/or free of Teflon and/or free of aromatic compounds, whereby it is even less problematic in handling and in disposal.

A suitable die can be provided for reshaping the fastening element and/or the workpiece. It can be static and, due to its shape, can result in the reshaping of said components when they are moved—e.g. by the setting device—relative to it.

In particular the fastening element and/or the workpiece and/or the die is/are wetted, in particular sprayed, with the lubricant at least in a region around a fastening point at which the fastening element is connected to the workpiece. In general, it is possible to apply lubricant to the components over a large area, for example, by dipping into a corresponding lubricant bath. However, a local application of lubricant in the critical regions is more efficient.

The die can have at least one opening, in particular a nozzle, by which lubricant can be supplied to the fastening point. In this case, a separate lubricant application device is often unnecessary.

The present invention also relates to a system for fastening a fastening element to a workpiece by means of a setting device, wherein the fastening element and/or the workpiece is/are at least sectionally reshaped during the fastening; and wherein a lubricant application device is provided that is adapted and configured to apply a grease-free and oil-free lubricant to the workpiece and/or to the fastening element and/or—if provided—to a die for reshaping the fastening element and/or the workpiece.

The present invention will be described in the following purely by way of example with reference to an advantageous embodiment of the invention and to the enclosed drawings. There are shown:

FIGS. 1a to 1c an embodiment of a method of fastening a rivet element to a sheet metal part in which an oil-free and grease-free lubricant can be used.

FIG. 1 shows three different states during a fastening of an (optional) internal thread 11 of a rotationally symmetrical rivet element 10 to a sheet metal part 12 by means of a setting device, not shown, that can have a conventional design. It is understood that rivet elements of a different design can also be used instead of the rivet element 10 and that they do not necessarily have to be rotationally symmetrical. Rivet elements having a bolt section—with or without a thread—are also conceivable.

FIG. 1a shows a starting situation before the fastening process, wherein the rivet element 10 is arranged above the sheet metal part 12 in FIG. 1a . A die 14 is present at the oppositely disposed side of the sheet metal part 12. The sheet metal part 12 is supported on spacers 16 that are fixedly connected to the die 14.

This means that the spacers 16 do not move in the course of the fastening process.

The arrangement of FIG. 1a is divided into two parts into a cross-sectional view at the left side and into a side view at the right side. The boundary between the two views extends through an axis of symmetry A that relates to the rotationally symmetrical rivet element 10, the sheet metal part 12—at least in a region around the fastening point—, and the die 14, as will be explained in more detail further below.

The spacers 16 extend in parallel with the axis A, wherein the spacers are, for example, screwed or inserted into corresponding bores 17 of the die 14 and are therefore releasably connected thereto. The spacers 16 are each made in the manner of pins and have an end section 20 that projects out of a contact surface 18 of the die 14. The length of the end sections 20 is set uniformly such that the sheet metal part 12 is horizontally supported on the spacers 16, i.e. perpendicular to the axis A. A spacing D is thereby set between a lower side 21 of the sheet metal part 12—i.e. the side of the sheet metal part 12 facing the contact surface 18—and the contact surface 18. Each end section 20 comprises a substantially convex support surface 22 facing the sheet metal part 12.

The spacing D can be adapted by an adjustment of the spacers 16 if necessary, e.g. if a different rivet element 10 should be used. The adjustment can, for example, take place by selecting a suitable screw-in depth or insertion depth (possibly bounded by an adjustable abutment) of the spacers 16.

The die 14 has a conical punch 24 that partly projects into a circular hole 26 provided at the sheet metal part 12. The axis A extends through the corresponding centers of the punch 24 and of the hole 26. In this respect, the axis A is thus an axis of symmetry for the sheet metal part 12—at least in the region around the hole 26—and for the die 14. The hole 26 was produced before the fastening process described here.

The sheet metal part 12 is planar in the region around the hole 26 and does not have a flare in this region. Optionally, however, the sheet metal part 12 can also be completely planar—as in the embodiment described here. However, this does not necessarily have to be the case.

A gap 30 is formed between a wall 28 of the hole 26 of the sheet metal part 12 and the lower side 21 of the sheet metal part 12, on the one hand, and the punch 24, on the other hand.

The rivet element 10 arranged above the sheet metal part 12 has a rivet section 32 that extends away from a flange section 36 of the rivet element 10 in the axial direction and that has an end edge 34 that is rounded at the outside and conical at the inside. A functional section that supports the thread 11 at least in part is provided at the other side of the flange sections 36. The rivet element 10 is a nut element.

A peripheral groove 38 is provided in a transition region between the flange section 36 and the rivet section 32.

The outer diameter of the rivet section 32 is slightly smaller than the diameter of the hole 26 so that the rivet section 32 can be inserted into the hole 26. Starting from the state shown in FIG. 1a , the rivet element 10 is now moved in the axial direction in the direction toward the die 14, wherein the rivet section 32 is aligned with the hole 26 of the sheet metal part 12 (coaxial alignment).

FIG. 1b shows the arrangement of FIG. 1a in a second state in which the rivet section 32 is inserted into the hole 26. On a further movement of the rivet element 10 in the direction toward the die 14, the inwardly disposed part of the end edge 34 of the rivet section 32 cooperates with a concave reshaping surface 40 of the punch 24 and the rivet section 32 is deformed radially outwardly so that the rivet section 32 engages into the gap 30 and engages behind the sheet metal part 12.

The rivet element 10 is displaced further in the direction toward the die 14 during the reshaping of the rivet section 32, wherein the flange section 36 comes into contact with a contact surface 37 at the sheet metal part 12. The length of the rivet section 32 or the spacing D is adapted such that the flange section 36 only comes into contact with the sheet metal part 12 when the rivet section 32 at least partly engages behind the sheet metal part 12 in the course of the reshaping, in particular when the reshaping that produces the engagement behind is completed.

The rivet element 10 is now moved further in the direction toward the die 14, wherein the sheet metal part 12 is moved along in the direction toward the contact surface 18 of the die 14. In this respect, the sheet metal part 12 is deformed locally in the region of the spacers 16 so that the end sections 20 of the spacers 16 engage into the sheet metal part 12 and the sheet metal part 12 comes into contact with the contact surface 18. In this connection, the end sections 20 of the spacers 16 that deform the sheet metal part 12 cause a respective elevated portion 41 of the sheet metal part 12 at the side remote from the die 14, as will be explained in more detail further below.

In FIG. 1c , the sheet metal part 12 is shown with the rivet element 10 after the completion of the fastening process. It can be seen that the sheet metal part 12 is deformed in the region of the rivet section 32 which engages behind the sheet metal part 12 during its movement from the position shown in FIG. 1b in the direction toward the die 14. In this respect, the region of the sheet metal part 12 originally adjacent to the hole 26 deflects due to a cooperation with the rivet section 32 that engages behind the sheet metal part 12 and that is pressed into the groove 38 of the rivet element 10. At the same time, the engaging-behind rivet section 32 is completely displaced into the plane of the sheet metal part 12 that extends perpendicular to the axis A by a cooperation with the reshaping surface 40 of the punch 24 so that the lower side 21 of the sheet metal part 12 facing the die 14 is substantially planar. This means that the reshaped rivet section 32 does not project out of the plane of the lower side 21. In addition, the rivet section 32 is deformed in part such that the rivet section 32 nestles against the sheet metal part 12. A particularly good shape matching and force transmission between the rivet element 10 and the sheet metal part 12 are hereby achieved.

As mentioned above, the end sections 20 of the spacers 16 engage into the sheet metal part 12 in the course of the movement of the sheet metal part 12 toward the contact surface 18 of the die 14. As a result, the already mentioned elevated portions 41 are thereby produced at the upper side of the sheet metal part 12 (FIG. 1c ).

To facilitate the insertion of the rivet section 32 into the hole 26 and the reshaping of the rivet section 32, an oil-free and grease-free lubricant is supplied. The lubricant at least sectionally wets the components involved in the fastening process—in particular in a region in which a reshaping takes place—, whereby the friction occurring between the components is reduced. This also results in a reduction of the loads occurring at the sheet metal part 12, at the die 14, and at the rivet element 10, which has a positive effect on the quality of the connection produced and reduces the wear of the die 14.

The lubricant can generally be applied to all the components involved. For example, provision can be made to initially only wet the rivet element 10, in particular the rivet section 32, with lubricant. Provision can additionally or alternatively also be made to supply the die 14 with lubricant in the region around the fastening point in order to support the fastening process. The same applies to the sheet metal part 12.

The lubricant can be provided by one or more suitable spraying apparatus which can be separate devices, for example. However, it is also possible to provide the die 14 and/or the contact surface 18 with at least one opening or nozzle not shown in FIGS. 1a to 1c through which the lubricant can be applied to the punch 24 and/or to the contact surface 18. It is also conceivable to effect a lubricant application through said opening to the rivet element 10 (in particular to the rivet section 32) and/or to the sheet metal part 12 (in particular in the region of the hole 26 and in adjacent regions). In this embodiment, these components are then—figuratively speaking—sprayed or sprinkled with lubricant by the die 14.

REFERENCE NUMERAL LIST

-   10 rivet element -   11 internal thread -   12 sheet metal part -   14 die -   16 spacer -   17 bore -   18 contact surface -   20 end section -   21 lower side of the sheet metal part -   22 support surface -   24 punch -   26 hole -   28 wall -   30 gap -   32 rivet section -   34 end edge -   36 flange section -   37 contact surface -   38 groove -   40 reshaping surface -   41 elevated portion 

1. A method of fastening a fastening element to a workpiece by means of a setting device, wherein at least one of the fastening element and the workpiece is at least sectionally reshaped during the fastening, and wherein a lubricant is used that is free of grease and free of oil.
 2. The method in accordance with claim 1, wherein the lubricant is a substance mixture of two or more substances.
 3. The method in accordance with claim 1, wherein at least one of the fastening element and the workpiece is at least partly metallic at least in a region around a fastening point at which the fastening element is connected to the workpiece.
 4. The method in accordance with claim 3, wherein at least one of the fastening element and the workpiece is completely composed of metal.
 5. The method in accordance with claim 1, wherein the fastening element is a rivet element.
 6. The method in accordance with claim 1, wherein the workpiece is a sheet metal part.
 7. The method in accordance with claim 1, wherein the lubricant is a water-soluble and/or water-based lubricant.
 8. The method in accordance with claim 1, wherein the lubricant comprises at least one of a corrosion inhibitor and a wear protection additive.
 9. The method in accordance with claim 1, wherein the lubricant is free of at least one of chlorine, Teflon and aromatic compounds.
 10. The method in accordance with claim 1, wherein a die is provided for reshaping at least one of the fastening element and the workpiece.
 11. The method in accordance with claim 1, wherein at least one of the fastening element, the workpiece is wetted with the lubricant at least in a region around a fastening point at which the fastening element is connected to the workpiece.
 12. The method in accordance with claim 11, wherein at least one of the fastening element, the workpiece is sprayed with the lubricant at least in a region around a fastening point at which the fastening element is connected to the workpiece.
 13. The method in accordance with claim 10, wherein at least one of the fastening element, the workpiece and the die is wetted with the lubricant at least in a region around a fastening point at which the fastening element is connected to the workpiece.
 14. The method in accordance with claim 13, wherein at least one of the fastening element, the workpiece and the die is sprayed with the lubricant at least in a region around a fastening point at which the fastening element is connected to the workpiece.
 15. The method in accordance with claim 10, wherein the die has at least one opening by which lubricant can be supplied to the fastening point.
 16. The method in accordance with claim 15, wherein the at least one opening is a nozzle.
 17. A system for fastening a fastening element to a workpiece by means of a setting device, wherein at least one of the fastening element and the workpiece is at least sectionally reshaped during the fastening; and wherein a lubricant application device is provided that is adapted and configured to apply a grease-free and oil-free lubricant to at least one of the workpiece and the fastening element.
 18. The system in accordance with claim 17, further comprising a die for reshaping at least one of the fastening element and the workpiece.
 19. The system in accordance with claim 18, wherein the lubricant application device is adapted and configured to apply a grease-free and oil-free lubricant to the die. 